The aims of the FIRCA application extend those of the parent grant by creating new opportunities (unavailable to the PI) to test hypotheses in living embryos for which the collaborating investigators - Dr. Maria Victoria de la Cruz and Dr. Ricardo Moreno - are uniquely experienced and qualified. The advantage of this approach is that it does not limit gene or protein expression to a single time point in any given embryo in which temporal characteristics must be interpreted by correlating information from static images obtained at different timepoints in different embryos. The collaborative investigators have the unique experience and talent to site direct vital markers including microbead carriers to incredible small primordial structures or to micrograft these structures to other embryos in order to trace the fate of a specific cluster of cells over time, in the same embryo and the morphological skills to interpret their integration into changing and complex phenotype. The relevance of this to the parent grant is that it provides a way to understand how in vivo the progenitor of precardiac cells - the heart forming fields - establish a segmented heart tube and if all regions of the embryonic heart are derived from this single source. The expertise of the collaborating investigator also gives us the chance to move testing of our hypotheses from primarily in vitro approaches to in vivo. Specifically, the aims of this Fogarty proposal collectively hold realistic potential to DIRECTLY reveal: the anatomical and molecular basis of cardiac segmental development, the unknown source of cells that give origin to the outlet of the heart and if a newly identified candidate segmentation gene we have called heart defect mediates their recruitment into a cardiogenic lineage, and finally if the abnormal integration or alignment of the primitive segments constitute common pathway by which many genes or environmental perturbations can lead to similar types of congenital malformation. The results of these studies would also have direct clinical relevance to the diagnosis and potential surgical treatment of life-threatening or life-compromising defects in newborn children.